Study of the mineral analysis of some gypsiferous soils in Salah al-Din and Najaf governorates using X-ray diffraction powder technique

Six soil pedons were selected, represented by the governorates of Salah al-Din and Najaf, distributed as three pedons for each governorate and located within a study path for each of them according to the geological formation, their physiographic location and the accompanying difference in sedimentation conditions resulting from the different sedimentation sources and the parent material. The results of the mineral examinations showed the predominance of light minerals for the very fine sand fraction in all horizons of the study pedon soils, and the evaporites were dominant in it, except for the exploited zarka region, which was characterized by the predominance of carbonate rocks. The results of the mineral analysis using the x-rays of the powder of the soil models, the absolute dominance of the minerals Quartz and Gypsum with different proportions and crystal sizes, respectively, in the surface and subsurface horizons of the Fursan pedon located within the soil of Salah al-Din with a relative rate of 51.53% and an average crystal size of 30.28 nm and a rate of 73.76% and an average size of 31.41 nm The surface and subsurface of pedon zirconia exploited for the pedons of Najaf, followed by Calcite, Feldspar, Dolomite and Aragonite in different proportion and sizes, in addition to the presence of other minerals such as rutile and various iron oxides such as Goethite and Hemetite.


INTRODUCTION
X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. About 95% of all solid materials can be described as crystalline. Soil mineralogy is studied routinely because of its strong influence on soil behavior, its use in soil classification, and its relevance to soil genetic processes. Soils commonly contain primary minerals, secondary minerals, and may have crystallographic characteristics that strongly influence the physical and chemical properties of soils.
X-ray diffraction is the technique which is most genuinely relied upon in soil mineralogical analysis (Chen 1988;Sullivan 1990). Jackson (1948) explained that the mineral interpretations of modern soils are important in studying soil formation processes for agricultural purposes, with the identification of weathering activities in both soils and sediments, as this requires studying the mineral content of the clay and non-clay part.
The same researcher, Jackson (1965) explained that the study of soil minerals is an important confirmation in understanding soil chemistry, because soil minerals, especially colloidal minerals, are very important for the exchange of positive ions, chemical weathering, and the liberation of nutrients in the soil. Many studies were conducted on the mineral composition of the Iraqi sedimentary soils, where Buringh (1960) explained that the differences in the mineral composition of the Iraqi sedimentary soils are due to the differences between the sediments of the Tigris and Euphrates rivers, which are due to the difference of their sources. (AL Rawi et al., 1967, AL Taie, 1968, AL Rawi et al., 1969 indecated that the mineral composition of the Iraqi sedimentary soils consists of Montmorillonite, Chlorite, and Mica minerals with some Quartz, Vermiculite, Palygorskite, Calcite, Smectite group and mixed minerals. Al-Muhaimid (1999) noted when studying sand minerals in their heavy and light parts in one of the sites near the Al-Raed research station located north of the Faculty of Agriculture in Abu Ghraib regarding the sovereignty, especially the light sand minerals, of which specifically, Quartz minerals were in all the study pedons, and he attributed this sovereignty to the resistance of this mineral to weathering due to the nature of its bonds Chemical As for Calcite, ranked second in terms of dominance, followed by Chert and Feldspar, and the percentage of Mica minerals decreased. The reason for the decline was attributed to the weak resistance of these minerals to weathering and their transformation into secondary minerals easily.
The aim of the current study is to compare the quantitative and qualitative content of different soil minerals and determine the extent of the difference in the crystal sizes of those minerals located within the sedimentations of the Tigris and Euphrates rivers. .

Geological of study area
The soils of the study area, especially the soils of Salah al-Din, are characterized by the presence of geomorphological phenomena in general related to their structural and geological status, as well as the occurrence of weathering and erosion processes soil pedon of Al-Fursan, which is located within the unstable pavement. The agricultural lands in this area are feed by water from wells that lie at depths of about 30 meters.
As for the University Pedon, which is exploited by wheat cultivation and sprinkler irrigation, it is also located within the upper terraces of the Tigris River at the beginning of the sedimentary plain and has a somewhat high topography interspersed with some valleys, As for the unexploited pedon Al-Alam (Arabs of China), located on the eastern side of the Al-Alam subdistrict, 16 km from the center of the city of Tikrit, it is an area of undulating gravel deposits of shallow gravelly gypsum soil known geologically as the accumulating plain.
As for the pedons of Najaf, including the pedons of Al-Zarka, which is exploited by cultivating various vegetables and by the runoff method and the unexploited, in the area of Al-Zarka(Khan al-Rub') on the road Najaf-Karbala, with a gypsum sedimentary origin ,While pedon the Bahr al-Najaf located in the village of (Abhoul), is described as a transitional area between the sedimentary plain and the Western Desert region, that is, between the stable pavement and the unstable pavement (Salloum and Sakr, 1994).

Diagnosis of light and heavy sand minerals
After the sand is separated from the clay and silt using a sieve with a diameter of 50 microns, the separated sand is taken after drying it by air, as the sand group is separated. The very fine sand whose diameter ranges between 50-100 microns and air-dried, and then it is ready to separate heavy and light metals by means of a separating funnel and by using bromoform liquid (CHBr3) with a specific weight of (2.89), after taking a certain weight of very fine sand (1 gm). ) is fixed on a glass slide by placing a drop of Canada balsam liquid. Light or heavy sand minerals are diagnosed and estimated by a polarized optical microscope according to (Kerr, 1959) and (Milner, 1962).

Minerological Analysis of Soil Powder
The analysis included the identification of non-clay minerals by X-ray diffraction for soil powder (XRPD), where the data were collected at a diffraction angle ranging from θ = 3 -50°2 with a step (θ 2) and at a speed of 16,000°/s. The peak areas were estimated by X-ray diffraction (XRD) based on the diffraction angle for each mineral, and the semi-quantitative estimates of the mineral ratios were calculated mathematically through the relationship between the area under the curve and the amount of difference in (2θ), and the Schiller equation was applied to calculate the crystallization volume. The samples were examined in the Ministry of Industry and Minerals (Iraqi Geological Survey) using the MAXIMA X-Ray DIFFRACTOMETER model 2009 of the Thetatype from the Japanese company SHEMADZU working with a Cu Kα (1.5418 A°) radiation tube at Kv40 and mA40.

RESULT AND DISCUSSION
The current study relied on diagnosing the mineral composition using the soil powder method (XRPD) for the surface and subsurface horizons of the coarse part represented by sand and silt particles for pedon soils. The results of the forms of X-ray diffraction 1-12 and the data of the X-ray diffraction results table1 indicated the variation of the predominance of minerals in the soil separated by horizons from the study pedons, and with different weight ratios depending on the In Salah al-Din soil, it was observed that quartz mineral predominated with a relative rate of 51.53% and an average crystal size of 30.28 nm within the surface horizon Ap and subsurface Bk of pedon Al-Fursan, with a value of 32.57% and a size of 28.1 nm in the surface horizon of Tikrit university. As for the Najaf soils, the results showed its dominance in the surface and subsurface horizon of the exploited pedons at a rate of 73.76%, with an average size of 31.41 nanometers, and the Cy1 subsurface horizon of the unexploited birch with a percentage of 34.33% and a size of 29.53 nm. Through these results, these ratios approximate with the ratios of quartz to the mineral composition separated by very fine sand for light minerals table.1, that possible diagnose its main peaks at an angle of 2θ = 26.67-26.74°. The high content of quartz in the sediments of the Tigris and Euphrates rivers, which is represented by the horizons of the soils of Salah al-Din and Najaf in general, can be explained by the high percentage mainly within the sediments from which those soils were formed, whether the sediments transmitted by water or wind erosion because it is characterized by its low specific gravity of 2.65, in addition as the main component of most soils, because it is the most common mineral in the earth's crust, in addition to its high resistance to weathering, which makes it more abundant in sand and silt parts (Senkyl et al, 1985). Therefore, it has a more stable crystal lattice. For the gypsum mineral, the main diffraction angle for it was determined at 2θ=11.45-11.73°. It was a clear superiority for the pedons located within the soils of Salah al-Din, especially the surface horizon A and the subsurface horizon By, belonging to pedon Al-Alam, at a rate of 40.13%, and with an average crystallization size of 27.8 nm, as well as at a rate of 33.39%, and with a crystallization size of 25.3 nm in the subsurface horizon Bky belonging to pedon University and with sharp peaks and elevated.
As for the Najaf soil, it distinguished be gypsum the as a dominant mineral in the surface horizon A of the unexploited pedon of Zarqa and the subsurface horizon of the pedon of the Sea of Najaf, it had a content of 33.50% and a crystal size of 27.55 nm and 40.77% and a crystal size of 31.80 nm respectively, in addition to that it is noted from The above results are the absence of a special diffraction angle for gypsum in pedon Al-Fursan belonging to Salah al-Din soil. This may be attributed to the low quantitative content of gypsum in those horizons, unlike the other horizons. Table2. The semi-quantitative relative abundance and crystallization size of the major (non-clay) minerals of the study pedon horizon soils nanometers. As for the pedons of Najaf soils, they were also of varying proportions and sequences between the same pedons or horizons, which were between the third and fourth, in order, except for Pedon the exploited Zarka and the surface horizon of pedon Bahr Al-Najaf. gave similar behavior to the soils of Salah al-Din in terms of the sequence diagnosed in general, As indicated light minerals there is a discrepancy in the feldspar content of the study soils, and according to the mineral sequence, it ranked third for the soils of Salah Al-Din, especially pedon the fursan ,its value reached by rate of 16.01% and average crystallization size of 29.7 nm and the surface horizon of the alam by 9 45% with a crystallization size of 27.33 nanometers. As for the Najaf soil, it was volatile and its content was somewhat less than that of Salah al-Din soil. In addition, a complete absence of this mineral was observed, as in the subsurface horizon of the exploited pedons. In general, its value The different oxides of the studied pedon soils were also diagnosed, and the values of each mineral and its basal distance d-spacing were determined based on the apparent diffractions with an X-ray diffraction apparatus. As for the hematite α-Fe2O3 for the soils of Salah al-Din, its appearance was observed in all studied horizons except for the surface horizon of pedon Al-Fursan. Its value was between 2.70-8.37%, with a relative rate of 6.10%, and with an average crystal size of 27.62 nm, lowest percentage on the subsurface horizonto pedon Al-Fursan and the highest value in the surface horizon to pedon university , while in Najaf soils its quantity was in the range of 2.67-8.46% with a rate of 6.01% and an average size of 27.73 nm. The lowest content in the surface horizon to pedon Bahr al-Najaf and the highest content in the subsurface horizon Cy1 to pedon. Unexploited Zarka.
These results are in agreement with the findings of Al-Jubouri , 2019 andBeauchmin et al., 2003 that the interconnected existence of these two minerals is often prevalent in the soils of dry and semi-arid areas, due to the characteristic in these regions of drought, lack of rain and high temperatures.
The results shown in Figures 1-10  ions.In addition, once frihydrite is formed, hematite is preferred over goethite with increasing temperature because dehydration involves the conversion of ferhydrite to hematite, as well that low influence of organic matter and increase in pH It led to the rise of the hemites at the expense of the goethites